Copper, cobalt, and ammonium sulfate recovery from mineral leach liquors



Aug. 4, 1953 P. J. MCGAULEY COPPER, COBALT AND AMMONIUM SULFATE RECOVERY FROM MINERAL LEACH LIQUORS Filed Jun Ore Conce/#refe ATTORNEY contain the copper, the nickel if. u v n and for certain types of leaching,.theiron if any Patented ug. 4, 19.53

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COPPER, OBL'II, AND AMRIONIUM SUL- FATE' RECOVERY FROM MINERAL 1 LEACH LIQUORS PatrickA J. Glen Cove, N.` Y., assignor to` Chemical Construction Corporation, New f `York, a corporation of Delaware Applicautiioune 4, y1949, serial No. 97,228`

rThisvinvention, is concerned withmtlie prodiicj tion of metallic metals from.,mixed oreconcentrates. It deals with processes in which,`, by

leaching, the metals values. ofore concentrates containing copper, cobalt and/orhnickelare,dis- ,solved therefrom and. subsequently recovered from the leach liquor.. YMore specically,'itlis concerned with the production of copperand'of f cobalt. In particulanit deals withthe precipitation of the cobalt metal powder. .Although ores containing cobalt, copper and/or nickel in` varying proportionsare 't not uncommon the `presently available methods of `isolating `the various metals values `thereofm'are not-.wholly satisfactory. Many oreswhich itmay be desirable to vtreat contain iron and the known procedures have no adequate provision` to deal therewith. ySome of the available processes are incapable of producing one or more of the metals `in yieldsof adequate quantity and qualitywhen the others are` present. In almost `all the known procedures, the economics ofthe necessary operationsresult in production costs rhigher than are desirable.

It is, therefore, the principal object of the present invention to devise a simple andV straightforward method for the production of cobalt in good yield and high quality from ores which lcontain copper and/or nickel and/or iron. Themetal product should be of sufficiently high/quality to meet `(zzornmercialqualifications and .the production should not be limited to the use ofthe undeysirable steps found necessary -infthecurrentyoperations. Such a process should noty be dependent upon any particular rtype of` ore.. `It, shouldlvinot require roasting and/or electricalprecipitation. It should not ,requireexcessively ,complicated process steps requiring" an unusual'..degree of `supervision nor shouldnt require i'iiiusual reagents or the use of extrao'rdinaryeqiiipnent.A

forward operationn A suitableore concentrate containing cobalt, usually accompanied by` copper and nickel and in` some cases iron, isleached by a suitable known method to place thecobaltl content in solution. yThe vleach.` liquor. will, also present,

is present. Iron Vis eliminated froinyt'hefleach liquor as waste. A` high `concern;rationf; of amu deals with the nitrate, 1. e., the ironand nickel-free residual liquor. The latter is treated as by boiling, etc., to precipitate the copper conftent as copper sulde. The copper-free liquor is `treated to separate out ammonium sulfate crys- "tals and build up the cobalt salt concentration.

' Finally, cobalt ammonium sulfate double saltis operation.

taken as illustrative.

crystallized from the concentrated cobalt liquor, redissolved andnally` cobalt metal is precipitated.

l.While presumably ores in which cobalt min- "eralsare the principal constituents may exist,

`they are certainly rare and do not represent the problems which must be overcome in an average The average yoriginal ore will fall within the class of materials discussed above. Because this is the most common situation, the treatment of such mixed ore concentrates is `j Furthenbecause the bulk of most orescnstitutegangue diluents, eifective operation requires .elimination of the latter. Accordingly, in average practice the original ore is treated in some way toreduce the gangue content. ThisY may beaccomplished in known ways, which form no part of the present invention, as by gravity concentration and/or froth `flotation andthe like.

In discussing 'the present process it is assumed `that some such operation has been carried out and`its is the resultant concentrate which is to be treated. 1 I

One or more of the metals may be present as an foxidized mineral although the greater part are usually sulfide `minerals.. It is i desirable, therefore, to'be able to treat both oxidized and sulfide minerals.' It is an advantage that the process of the present invention is readily adapt- '.'able to the Atreatment of both. Because the problems involved are typical, a concentrate cont 4o" In general, the process requirements ofthe `present invention have beenrnetin` a` straight# taining copper, iron,` cobalt and nickel will be Luse'd as illustrative in this discussion.

Inorder to more easily understand the-flow of i thepresent invention, reference is made to the faccompanyingdrawing. `The latter constitutes a simplified flowsheet showing themajor steps with which the present invention is concerned .jand their relation to the treatment of the remainder of the ore.

, Leaching procedures to place the metal values u an artwhich is highly developed. So far as the vvmetallic nickel preparation of the present inmonium sulfate is formed VinE the liquorfand l f nickel is quantitatively` precipitated'therefrom 4,asa nickel ammonium sulfatedouble salt.

The Partiular, process .ofthefpresem triplicaof `such an ore concentrate in solution also form.

lv entionis concerned, the exactjleachin'g procei dure used"may be widely varied. Perhaps the 55.4

vmost common procedures involve either acid,

usually sulfuric, or ammoniacal leaching, with or without concurrent oxidation, depending upon the oxides and suldes content of the ore being treated. The present invention is applicable to an ore being treated'by any of such'jprocedures Because the invention is not limited to a particular type of leaching, in the drawing this operation has been designated generically as a leaching system. Leaching vis vordi'r'iarilyy carried out in some multiple tank" system, the; exact arrangement of which is not a critical factor in this application. The copper; iron-., cob alt,

and nickel-bearing concentrate is fed thereto,

and is treated therein with one or more suitable leaching agents. These may be any suitable acid or ainmoniacal leaching liquors` and' lthey are' used in a known manner. Several different leachingmethods arewell known.

The residualbarren solids may be passed to waste. In ,most cases they will containl the gangue diluents." In addition, Where ammoniacal orother leaching liquors of high pH are used the iron will report here. Any iron which may have been oxidized willbe precipitated as ferric oxide or hydroxide, insoluble at 4the high leachngp,

A lleach liquor Vcontaining the dissolved Ametal values is drawn from the leaching system. In usingmosttypes of acid leaching, particularly Where oxidation isl employed, there will be a considerable content Aofwdissolved iron. This must be eliminated from the solution. I have found that thewiron-can be caused to precipitate from a concentrated ammonium salt solution at a suitablev while keeping the other metal values in solution., l n

Accordingly, the pH ofV the pregnant leach liquor isadjusted to about 3- 4. Because of the oxidation which is a normal step of average operation upto this point, the dissolved iron will be in theuferric condition.V At thesel pHs, it will precipitate, and may be filtered out as oxide or hydroxide andhplassed to waste. n

Neutralization may be carried out in any desired mannerh For example, it maybe v*done by theaddition of ammonia to a sulfuric acid leach liquor or by the addition of sulfuric acid to, or by theV formation of Ysulfuric acid in situ in, an ammoniacal leach liquor. Where the problem of ironis not involved, this pH adjustment and the removal of the resultant iron precipitate may be eliminated if so desired. This is indicated in the flowsheet as an optional flow by a dotted line.

Further, in accordance with the work done in developing the present invention, it was found that at a pH of about 4.0-6.4 in a concentrated solution of ammonium sulfate the nickel content of a solution can be precipitated quantitatively as a nickel-ammonium sulfate double salt. At the same time, other metals, i. e. the cobalt and copper in the illustrative case, can be retained in solution.` Accordingly, the iron-free, metalsbearing'leach liquor is treated to bring'it into this condition,

Whether a sulfuric acid leach or an ammoniacal leach is used, any pH adjustment, i. e., that performed previously to remove iron and/or that done at this point to precipitate the nickel double salt Will result in the formation of a considerable amount of ammonium sulfate. This will usually bel suflicient'for the purposes of the present inven'tior'i.v If not,1 additional preformed ammonium sulfate'may be'added. This latter"'causes no particular problem since, as Will be brought out 4 below, ammonium sulfate is one of the usual products of the process.

The resultant slurry is filtered to separate out the precipitated double salt. Qrdinarily the presscake is washed. TheI washing's'may .be either added to the'ltrate or, if sod'esired, optionally returned to the leaching system. The filtrate and the double salt presscake are separately treated;`

Nickel values, which are contained in the presscake,` 'are' recovered in a nickel recovery system. The latter, which forms no part of the present invention, maybe operated in any desired manner. Accordingly, it is simply designated under the generic term nickel recovery system." An excellentl system for the purpose forms the subject-matter of my copending application for United States Letters Patent, Serial No. 97,227, filed of evendate. So far as operating the process ofthe present invention is concerned, 'it is sufficient `to n ote that such al system produces a nickelV product, preferably `as, precipitated' metal powder, anda nickel-bearing mother liquor. The latter is recycled, ordinarily to the leaching system; In someA cases Vthere lmay bean iron salt, or iron oxide'or hydroxide discard.

Treatment of the'filtrateA and washin'gs constitutes the primary feature of the present application. With'or ywithout all or a part of the washings, it is boiled'for a sufficient 'time to precipitate 'the copper content las copper sulfide. Colloidal sulfur will fordinarily be conjointly precipitated. The copper'precipitation may be considered. as complete for all practical purposes. Accordingly, the slurry is filtered and the'solid residue 'which comprises'the' presscake is sent to a copper treating cycle. The filtrate will coritain ammonium sulfate which vis separated out and recovered. Cobalt, if anyis present, is isolatedfrom the filtrate ina vcobalt recovery cycle. These vthreev operations constitute the u filtrate treatmentwhich is the subject of the present invention. u n

While it is possible to treat thev copper sulfidesulfur presscake by other means, an adequate and suitable procedure has been developed in the present process in accordance `with the following steps: The. residue is leached to r'edissolve the copper content. This may be carried out with any suitable leaching agent. While for most purposes it may be 'desirableto use aqua ammonia,fit is feasible if so desired to use acidic leaching. In'either case, `concurrent oxidation by oxygen and/or air is desirable.

Againthe operatingv temperature and pressure used to convert'sulfides to sulfates during leachingis not critical and affects'primarily the time required. 4The operation" may-be carried: out, therefore, in any suitable vvessel at any convenient' temperature' and pressure. lWhere an acid leaching is used itv may bedesirable to bleed'steam from the operation'in order'to prevent the temperature and pressure'rise from becomingl excessiveI dueto the exothermic reaction. About *325 ic. wiiiordiriarii'y constitute a practical upperV lterriperature limit ,un'dertheseI conditions. While higher temperatures may be used, if desirable' o'r necessary, they may require stronger apparatus` than isV usually available.

After leaching, regardless of vthe nature of the leaching agent, theslurry is filtered to remove the `sulfur and'any other `solids'which may be present.vv Sulfur may be recovered as a saleable product,I if so desired', by melting, lfiltering and cooling. The resultant copper-bearing liquor `rl'ected by some conventional means such as a `centrifuge or the like, and constitute one of the may vary considerably in purity. L If 'suciently pure, it may be passed directlyto a copper red'ction cycle. However, the eventual production of :copper metal powder in high quality requires precipitation 'from quite pure copper liquor if ithe yield in any one cycle is to be practical. Acfcordingly, wherever necessary, the copper solu- 'tion, `after the sulfur and solids removal is Ipuried. y e

Purification of the copper solution may take any one of a number of forms. While other treatments may be used, a preferred procedure is to crystallize the copper content ascopper sulfate. This may require elimination of part of the water and a pH adjustment in some cases. A heated, substantially saturated solution is 'prepared and the copper salt thrown out of solution by cooling and collected. The resultant cop'- per sulfate is redissolved and subjected to treatment' to precipitate the copper content as metal powder.

Like the copper solution purification, the reduction may be carried out in any suitablefway. The copper solution is preferably combined with sufficient low-grade copper metal to insure` reduction of all cupric ions to the cuprous condition andthe mixture is saturated with a reducing gas'such as icarbon monoxide. The resultant slurry is then treated under increased temperature and pressure in a reducinggas atmosphere to rcomplete the reduction of copper to a metallic condition.

ASince the product powder, in order to be commercially desirable, must be at least 99.9% pure, with the possible exception of silver and oxygen, precipitation must not be carried beyond the stage where any precipitatable extraneous metal ions in the solution approach a 1:1 ratio with the copper in solution. Where precipitation is from an acid solution, it is ordinarily desirable to stop the precipitation at about 70% precipitation of the avail-able copper although if the solution is known to be sufliciently pure, precipitation may be carried much further. When precipitation is from basic ammoniacal liquor, a larger amount of copper is preferably left in the mother liquor in order to provide copper-ammonium complex ions for vthe next leach cycle. Only about 2040% of the available copper ordinarily will be precipitated yfrom such liquors.

The copper metal powder product is separated out and collected. Any'residual copper solution other than that required in the 'next succeeding purication and reduction steps is recycled vto the leaching system. There is no eventual loss of copper and for the average cycle a mol of copper product is obtained for each mol of copper dissolved from the concentrate, For this reason, als-o, it is desirable that the` same type of leaching agents be used in the copper precipitation 'cycle as was used in the original leaching ,system although this is not a necessary limitation on the overall process. j

Filtrate, after removal of the copper sulfideysulfur residues; is sent to an ammonium sulfate crystallizer. This may operate in a conventional manner, utilizing a temperature differential and/or evaporation to precipitate ammonium sulfate crystals. The latter are removed and colsaleable products.' Product ammonium sulfate "may be used if desiredor necessary in the `above Iknoted-nickel double salt precipitation. Y As-*wasnoted above, cobalt, if present-is in l thecopper-f'ree liltratefrom whichfthe airline-1 nium sulfate is crystallized. 'With most `ores the will be almost necessarily so'whereinickel has been initially removed because the cobaltand copper ratios j'withrespec't to the nickel and the amount of ammonium sulfate in solution will have been'maintained at values at which the cobalt remains entirely dissolved. e i

Accordingly, ammonium sulfate crystallization is at any one time carried only to the extent that no cobalt salt willbe precipitated therewith. The cobalt content is thus built up until it approaches the'content at which crystallization o f cobalt salt Will begin at the operating temperature. At this cobalt content, mother liquorl is drawn from the VammoniumA sulfate crystallizer to a cooler-crystallizer in which cobalt-ammonium sulfate double salt can be dropped from solution with `a minimum content of ammonium sulfate per se. The residual liquor is returned to the ammonium salt crystallizer.

In starting up operations, mother liquor is ordinarily not passed through the cooler-crystallizer until the cobalt content is built up to a concentration at which precipitation of ,cobaltammonium sulfate occurs.' Mother liquor of reduced cobalt content is returned t0 the ammonium` sulfate crystallizer. Some ammonium sulfate will crystallize with the cobalt-double salt.

Preferably, but notnecessarily, this operation is carried out at a pH of about 3.5-5.5 under which conditions cobalt is present as a cobaltammonium sulfate double-salt and the latter can be precipitated as completely insoluble in a sunlciently concentrated ammonium sulfate solution. Under the operating conditions this ammonium sulfate content is present. I Y

Precipitated cobalt double salt crystals are col'- lected and redissolved. This should be donenby adding sucient ammonia or aquav ammonia to produce a pH above 5.5, at which values the 'cobalt-ammonium complex ion forms and the cobalt-ammonium double saltis completely dissolved and converted to this condition.V

i If the amount of ammonium sulfatev and/or other impurities may be considered to be negligible, the resultant solution may be passed directly to `a cobalt reduction step. However, this seldom occurs. Accordingly, the cobalt-ammonium complex salt solution usually is subjected to oneor more purification operations. For example, lime is ordinarily added to precipitate the excess sulfate ions as calcium sulfate which are removed by a suitable filter. If' so desired, the cobalt-ammonium complex salt may be further purified either per se or after conversion to cobalt sulfate by crystallization. Ordinarily, this willnot be necessary.

f1' Finally, the purified cobalt solution is subjected to reduction. This is carried out in a solution saturated with a reducing gas such as carbon monoxide at any convenient temperature and pressure. It is an important feature of the present invention that this,A precipitation and reduction is preferably' carried out from a `solution of the cobalt as cobalt-ammonium complex ions. Itcannot be effectively carriedout from 4'any other solution unless'provision `ismade, to jeliminatethe hydrogen ions formed' during re- Tduction.

vPrecipitation' ,is` carried out Yonly ofthe extent.

thatthe cobalt is precipitated inksufcieht purity..

solved cobalt content approaches the cobalt sulfate-ammonium sulfate double saltl saturation point at the operation temperature; removing the ammonium sulfate crystals; withdrawing and cooling cobalt-concentrated mother liquor sufciently to precipitate at least part of the dissolved cobalt and ammonium sulfate double salt, collecting precipitated salt and returning the residual mother liquor to the ammonium sulfate concentration step for further cobalt concentration.

5. In separating cobalt from an aqueous ammoniacal ammonium sulfate solution containing sulfates of cobalt in minor amounts, the steps which comprise: adjusting the pH to from about 3.5 to about 5.5 and removing water sufciently to cause crystallization of ammonium sulfate; continuing said concentration and crystallization until the dissolved cobalt sulfate-ammonium sulfate double salt content approaches its saturation point at the operation temperature and removing References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,686,391 Muller et al Oct. 2, 1928 2,356,183 Shepard et al. Aug. 22, 1944 2,520,958 Poole et al. Sept. 5, 1950 2,526,707 Stahl Oct. 24, 1950 2,576,314 Forward Nov. 27, 1951 

3. IN THE TREATMENT OF SOLUTIONS OBTAINED BY OXIDATION LEACHING OF SULFUR-BEARING MIXTURES CONTAINING NICKLE, COBALT AND COPPER WHEREBY SUL FATES OF METAL VALUES ARE DISSOLVED, THE METHOD OF SEPARATING THE COBALT CONTENT OF THE SOLUTION WHICH COMPRISES: ADJUSTING THE PH OF THE SOLUTION TO FROM ABOUT 4-6.5 AND THE SULFATE CONTENT TO THE EQUIVALENT OF SOLUTIONS AS ABOUT 25* C. CONTAINING CONCENTRATIONS OF (A) COPPER AND COBALT NOT OVER ABOUT 10% AND 6% RESPECTIVELY AT ABOUT 10% AMMONIUM SULFATE AND 2% AND 1.3% RESPECTIVELY AT ABOUT 20% AMMONIUM SULFATE, AND (B) AMMONIUM SOLFATE OF AT LEAST 9%, AT WHICH SUBSTANTIALLY ALL OF THE COPPER AND COBALT REMAIN IN SOLUTION AND SUBSTANTIALLY ALL NICKLE PRECIPITATES; REMOVING ANY NICKLE-BEARING PRECIPITATE; HEATING THE RESIDUAL SOLUTION SUFFICIENTLY TO PRECIPITATE SUBSTANTIALLY ALL OF THE COPPER VALUES; USE AND REMOVING THE PRECIPITATED COPPER VALUES; ADJUSTING THE PH OF RESIDUAL LIQUOR TO ABOUT 3.5-5.5 AND MAINTAINING THIS ACIDITY; CONCENTRATING ADJUSTED LIQUOR TO CRYSTALLIZE AMMONIUM SALT THEREFROM, CONTINUING AMMONIUM SALT CRYSTALLIZING UNTIL THE COBALT SULFATE-AMMONIUM SULFATE DOUBLE SALT CONTENT APPROACHES THE SATURATION POINT AT THE OPERATING TEMPERATURE AND COLLECTING RESULTANT AMMONIUM SALT CRYSTALS; AND CONTINUOUSLY PASSING CONCENTRATED COBALT MOTHE LIQUOR TO A COBALT COOLER-CRYSTALLIZER, WHEREBY COBALTAMMONIUM SULFATE DOUBLE SALT IS CRYSTALLIZED, COLLECTING COBALT SALT CRYSTALS AND RETURNING RESIDUAL MOTHER LIQUOR TO THE A MMONIUM SALT CRYSTALLIZED TO BE FURTHER CONCENTRATED IN COBALT. 